What is the Boundary Scan device Normal Operation mode?

Boundary scan normal operation mode

When the device is operating under the normal mode, the boundary register is transparent. Signals can pass through the boundary scan cells freely and the device operates as it would without test cells. In this mode, test data is captured in the boundary register cells, then shifted through the boundary register out to TDO.

While in normal mode, SAMPLE/PRELOAD, BYPASS, IDCODE, USERCODE and possibly a manufacturer-supplied function can be executed.

SAMPLE must be executed in normal mode because, as the name implies, the test takes a sample of the data present in the device at a specified time. The sample is subsequently shifted out for examination.

PRELOAD sets the output register cells to a specified data pattern prior to the selection of another boundary-scan operation. (SAMPLE/PRELOAD is one instruction that performs two functions.)

BYPASS selects the one-bit register path so that data can be shifted through the device more quickly during scan operations.

IDCODE and USERCODE verify device and manufacturer identification and device application. These functions are explained in more detail in the following section.

Figure 1 illustrates the status of the boundary register cells during normal operation mode. The red line shows how signal flows during normal operation mode. The yellow lines show how a sample is captured. The green line shows the path for shifting the captured sample data out.